|From:||Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>|
|To:||PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org>|
|Cc:||Andres Freund <andres(at)anarazel(dot)de>|
|Subject:||raised checkpoint limit & manual checkpoint|
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The checkpoint time limit has just been raised to one day after a
discussion started by Andres Freund:
I would have gone further up, say one week or even one month, but I think
that this new limit is an improvement over the previous 1 hour maximum.
Now ISTM that there is a possible use case which arises with this new
setting and is not well addressed by postgresql:
Let us say that an application has periods of high and low usage, say over
a day, so that I want to avoid a checkpoint from 8 to 20, but I'm okay
after that. I could raise the size and time limits so that they do not
occur during these hours and plan to do a manual CHECKPOINT once a day
when I see fit.
Now the problem I see is that CHECKPOINT means "do a CHECKPOINT right now
as fast as possible", i.e. there is no throttling whatsoever, which leads
to heavy IO and may result in a very unresponsive database.
I would suggest that a good complementary feature would be to allow a
manual checkpoint to run over a period of time, say something like:
CHECKPOINT OVER '10 hours';
That would target to complete after this period (whether it succeeds or
not is another issue) instead of going as fast as possible, thus avoiding
some performance degradation.
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